What should have been a moment for celebration was quickly turned into one for contemplation. Celtic had only just clinched a historic Treble Treble (three straight seasons of three domestic trophies) when then-interim manager Neil Lennon was offered the job permanently by club chief executive Peter Lawwell. With that, all chat turned away from what had just been achieved and toward what could be lost.

Lennon is a Celtic legend. For many he is the best embodiment of the Glasgow club in its modern form having won titles as both a player and manager. But drafted in as a stop-gap solution following the surprise exit of Brendan Rodgers to Leicester City in March, Lennon’s second coming split opinion among the Celtic support.

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Celtic finished the 2018-19 season with three pieces of silverware in their hands, but in the eyes of many, they staggered over the finish line. Under Lennon, their play became more disjointed, more stilted. The Hoops grew more reliant on moments of character and team spirit — late fightbacks and stoppage-time winners. Most agree there has been a certain degree of deterioration.

It’s for this reason that Celtic face their most important preseason in years. This season, more than any other in recent times, there can be no room for deterioration. Steven Gerrard has given Rangers a platform to truly challenge Celtic for honors at the top of the Scottish game with many predicting a title race for the first time in the best part of a decade.

For Rodgers, there was a margin for error. His Celtic team set a relentless pace at the top of the Scottish Premiership, but perhaps they were able to do that comfortable in the knowledge that a slip-up could be absorbed. Now, however, that margin of effort is narrowing. Celtic remain Scottish football’s predominant force, but their supremacy is no longer a given.

Part of the problem Lennon experienced upon taking over last season was a philosophical one. Rodgers is a coach who favors possession-based play that is quick through the lines of transition. Lennon, on the other hand, is more of a traditionalist. His teams play a more direct game. He wants Celtic to play with old-fashioned wingers and emphasize crosses into the box.

At present, though, Celtic’s squad isn’t built to play this way and so there was a disconnect between Lennon’s tactics and the traits he inherited in his players. That must be addressed this summer. If Celtic are to continue their march to 10 league titles in a row, they must alter their squad to Lennon’s specifications.

This isn’t to say the Scottish champions don’t already boast a highly talented squad. In Kieran Tierney, they have a left back tipped as potentially world-class and the subject of much interest from Arsenal this summer. Kristoffer Ajer, in many ways, has the look of a Norwegian Virgil Van Dijk, possessing many of the same qualities that made the Dutchman such a hit during his time in Scotland.

Callum McGregor was arguably the Celtic player who grew the most under Rodgers. Indeed, the heartbeat of the Celtic team can be felt in the movements of the 26-year-old with his former manager reportedly interested in luring the midfielder to Leicester City. Then there’s James Forrest, a once mercurial winger who has become incredibly consistent in recent seasons. And Odsonne Edouard, the 21-year-old center forward compared to Moussa Dembele, the former Hoops striker now proving a success for Lyon.

Rangers have already made a number of additions, some very impressive, this summer, but Celtic’s squad remains the best balanced and most accomplished in Scotland. Lennon has a lot to work with, so there can be no excuses if the Hoops fail to meet the standard set over the past eight years. 

These friendly fixtures, starting with Tuesday’s game against St. Gallen, will provide the first real glimpse of what Lennon envisages for his Celtic team going forward. He has had time to impose his own ideas on this group of players with a number of new signings also made. It’s over the coming weeks that judgements will be made ahead of the most anticipated Scottish Premiership season in years. 

Lennon doesn’t have much time to get things right. Celtic’s season will partly be defined by their success or failure in the Champions League qualifiers they face later this month. They are arguably their most important fixtures of the season, and they come when so many moving parts are still to settle. For more than one reason, there is a lot riding on Celtic’s preseason.

Graham Ruthven is a soccer writer based in the U.K. He has written for the New York Times, Guardian, Eurosport, Bleacher Report, and others.